Marcos L. Dias

Porous structure and swelling properties of styrene–divinylbenzene copolymers for size exclusion chromatography

Small spherical particles of styrene–divinylbenzene copolymers have been synthesized by modified suspension polymerization. The effects of divinylbenzene (DVB) contents, dilution degree of the monomers and diluent composition on the porous structure and swelling properties of the copolymers were investigated. Toluene uptakes of macroporous copolymers were considered as a result of three contributions: filling of the fixed pores, expansion of the fixed or collapsed pores, and nuclei swelling and heptane uptakes as a result of the two first contributions. The increase of DVB content in the copolymers synthesized in presence of a solvating diluent (toluene) provoked a decrease on the nuclei swelling. The increase of dilution degree with solvating diluents changed the toluene and heptane uptakes, and when the diluent–copolymer affinity was reduced, the fixed pore volume increased.

Comparative study of shear degradation of carboxymethylcellulose and poly(ethylene oxide) in aqueous solution

Abstract Shear degradation of sodium carboxymethylcellulose (CMC) and poly(ethylene oxide) (PEO) was investigated in aqueous solution. Experiments to evaluate the degradation consisted of preparing the polymer solution, shearing it in a capillary viscometer and analysing the viscosity and polymer molecular weight of the samples collected before and after the high shearing. Changes in the number- and weight-average molecular weights were monitored by size exclusion chromatography. Polymer concentrations from 1 to 4 g/l, shear stresses from 500 to 1900 Pa and temperatures of 30 and 50 °C were used as experimental conditions. CMC molecules did not degrade in any of the conditions employed. Decreasing viscosity of the CMC solution after shearing was not considered to be due to molecular degradation but to the breaking of macromolecular aggregates. PEO molecules, which are more flexible than CMC molecules, degraded in the same conditions used for CMC. Degradation increased as shear stress and polymer hydrodynamic volume were increased. Changes in concentration also influenced the degradation. The effects of concentration were attributed to changes in the hydrodynamic volume. No influence of temperature on the shear degradation of PEO was observed. In solution, PEO molecules degraded even if molecular entanglements were absent.

Alginate microparticles as oral colon drug delivery device: A review

The increase in the research interest on alginate microparticles in pharmaceutical and biomedical areas confirms its potential use as an effective matrix for drug and cell delivery. Among the well known alginate properties, pH sensitivity remains as an attractive option for targeting of drug in the colon region. This essential aspect is advantageous to enhance therapeutic efficacy of treatment of inflammatory bowel diseases, which require multi-drug administration frequently in a long period. As consequence, severe side effect appears leading to discontinuation of therapy and affecting quality of patient life. This review gives an overview of relevant properties of alginate as oral colon delivery systems and the recent innovative strategies of using alginate with other polymers as well as microencapsulation techniques. At the same time, it describes the several advantages of coating processes involving alginate over microparticles in order to design better material with sustained release characteristic for colon-targeted delivery.

Reactive Processing of Nylon-6 and Triphenyl Phosphite. I. Molecular Weight Changes

Nylon-6 chain extension by means of reactive processing in the presence of triphenyl phosphite (TPP) was investigated using an internal mixer coupled with a torque sensor. The molecular weight was dependent on TPP concentration, processing time, polymer drying conditions, rotational speed and processing temperature. The molecular weight greatly increased after TPP addition. The highest values were observed when 3 wt% of TPP was added to the polyamide. Polydispersity increased as a function of the amount of TPP. The higher the TPP concentration, the higher was the polydispersity. Long processing time, high rotational speed and high processing temperature led to the lower M w values. The degree of crystallinity of nylon-6 was slightly reduced when the polyamide was processed in the presence of TPP at 80 and 100 rpm and 280°C.

4-Vinylpyridine polymerization with soluble catalysts

Abstract Homopolymerization of 4-vinylpyridine (4-VP) was performed using different soluble catalyst systems. The results of 4-vinylpyridine polymerization with Ti(OC4H9)4; TiCl4·2THF; Cp-TiCl3 − Cp = η5 − C5H5 and Ni(acac)2 − acac = acetyl acetonate as catalysts activated by methylaluminoxane (MAO) are reported.

Rheological behavior of poly(lactic acid)/synthetic mica nanocomposites.

Poly(lactic acid) nanocomposites were prepared with three synthetic fluoromicas in a twin-screw extruder. Sodium and two organomodified synthetic fluoromicas at different compositions were used. The effect of mica type and composition on the rheological behavior of the nanocomposites was evaluated. The sodium fluoromica did not have a significant effect on the poly(lactic acid) rheological properties, while addition of the organophilic micas to poly(lactic acid) has a strong effect on the rheology, showing a pronounced shear thinning behavior. The dynamic rheological studies revealed that the nanocomposites with organomica have a higher viscosity and more pronounced elastic properties than neat poly(lactic acid). Both storage and loss moduli increased with mica content.

Miscibility of PET/PC Blends Induced by Cobalt Complexes

Amorphous miscible PET/PC copolymers were prepared by blending the two constituent blend homopolymers at 50/50 wt% proportion in presence of cobalt acetylacetonate II and III (0.05 and 0.1 wt%) in the molten state. The reaction products were evaluated by solubility in methylene chloride (CH2Cl2), differential scanning calorimetry (DSC), thermogravimetry (TGA), and Fourier transform infrared spectroscopy (FT-IR). Two fractions were obtained by extracting the blend with CH2Cl2: one soluble, rich in PC, and another one insoluble, rich in PET. The DSC showed a unique glass transition temperature (Tg) (around 100°C) and the absence of melting temperature peak of PET, indicating that an amorphous copolymer was obtained. The Tg value coincides with Fox and Couchmans calculations and indicates the formation of a miscible system. TGA curves of the blends showed thermal degradation between that of the homopolymers. FT-IR showed a decrease of PC carbonyl band at 1773 cm−1, a broadening of PET ester carbonyl band at 1720 cm−1, a decrease of PET degree of order and a new band at 1063 cm−1 attributed to the formation of aromatic-aromatic ester structure in the copolymer. The composition of CH2Cl2 insoluble and soluble phases were determined by FT-IR from calculation using the molar absorptivity of PC p-disubstituted ring band (558 cm−1) and Lambert-Beers law. The results indicated that exchange reactions took place, predominantly alcoholysis and acidolysis, and were to some extent dependent on the type and amount of cobalt complexes.

Core Shell Silica-Silicon Hybrid Nanoparticles: Synthesis and Characterization

Silica-silicon hybrid nanoparticles completely soluble in hydrocarbon were prepared by copolymerization of tetraethoxysilane (TEOS) and alkylethoxysilanes like methyltriethoxysilane (MTEOS), dimethyldiethoxysilane (DMDEOS) and dimethoxydiphenylsilane (DMODPS) by using the sol-gel process catalyzed by ammonium hydroxide in ethanol and methanol. Control of surface chemical structure and solubility was achieved by introducing trimethylchlorosilane (TMCS) as polymerization terminator. Nanoparticles with diameter in the range of 10 to 52 nm were obtained. The structure and thermal stability of the nanoparticles were highly dependent on the reaction condition. Higher conversion of hydrocarbon soluble silica-silicon nanoparticles were attained using water:Si molar ratio close to 9. The hexane soluble nanoparticles present hydroxyl and methyl groups on the surface. Wide angle X-ray diffraction and Si solid state NMR show evidences that these silica-silicon hybrids presents a core-shell structure with a core constituted by SiO2 and a shell formed by methyl or phenyl siloxane. The material can be applied to prepare different types of silica-silicon hybrid membranes.

Size exclusion behavior of polymers in amide solvents — III. Elution characteristics of acrylic polymers in N,N-dimethylformamide

Nonexclusion effects of acrylic polymers in the size exclusion chromatography using DMF as the mobile phase were investigated. A poly(methyl methacrylate) sample containing sulfate terminal end groups presented marked differences in the elution behavior when compared with the corresponding neutral sample, as in the case of polyacrylonitrile (PAN). It was observed that there is an unexpected small retention in the PS-DVB column and a large peak was detected by UV at 280 nm, which was not detected by the RI detector. The deionization of the DMF extinguished the peak detected by UV and shifted the retention volumes to higher values, but it did not affect the shape and position of the neutral polymer peak. A very strong adsorption effect was shown in the SEC of poly(acrylic acid) (PAA) in deionized DMF. The activity of the sites on the PS-DVB gel in deionized DMF was suppressed by saturation through successive injections of PAA. The elution peculiarities were ascribed to the electrostatic interaction between the charged polymer chains and the ionic species from DMF degradation. The addition of a small amount of LiBr to DMF inhibited the interactions completely.

Morphology and thermal properties of polyethylenes made by metallocene and Ziegler-Natta catalysts

Abstract Morphology and thermal behavior of high density polyethylene and ethylene-octene copolymers prepared with classical Ziegler-Natta (zHDPE) and metallocene catalysts (mHDPE and mLLDPE) are comparatively discussed. Wide angle X-ray diffraction (WAXD) data at room temperature showed that mHDPE crystals are more perfect with smaller unit cell dimensions and have higher crystalline density and larger crystallite sizes when compared to zHDPEs. In the case of copolymers, the unit cell dimensions did not change significatively when the number of branches was increased. Average interplanar chain distances in the amorphous phase increased with increasing octene content in the copolymer, showing a marked influence on the packing of the amorphous phase and confirming that the branches are concentrated in this phase. The existence of second phase in the ethylene-octene copolymers prepared with metallocenes was identified by calorimetry. The existence of this phase is time-dependent and was interpreted as the result of hexyl branches ordering in the amorphous phase. A morphological model based on Vile three-phase model, WAXD results and calculations involving empirical equations for fold and extended chain lamellae crystals was proposed to explain the time-dependent thermal behavior of these copolymers.